Do You Need to Wear Sunscreen Indoors? An Analysis

Dr. Michelle Wong—chemist, science educator, and cosmetician—explains the science:

Factors to take into account

UVA and UVB aren’t entirely interchangeable, so it’s important to know what you’re up against.

Sunscreen is rated by SPF, which indicates UVB protection—guarding against burning, skin cancer, and premature aging. Broad spectrum or UVA ratings measure protection against UVA rays, which cause tanning, contribute to melanoma, and can lead to skin aging and hyperpigmentation. However, most UV studies are based on white skin, which may not apply universally.

The need for sunscreen indoors depends on how much UV exposure you receive there:

• Direct exposure occurs when sunlight shines directly on you, such as when sitting by a window.
• Diffuse exposure happens when UV rays are scattered by air molecules or reflected off surfaces, which can still occur in shaded areas.

Indoors, walls and barriers do reduce UV exposure significantly. However, factors like window size, distance from windows, and the type of glass (which blocks UVB but not all UVA) play important roles in determining exposure.

The UV index (your phone’s weather app will probably have this) indicates the level of sunburn-causing UV in a specific area at a particular time. In Sydney, for example (where Dr. Wong is), the UV index can vary from 12 in summer to 2 in winter. Although UVA levels fluctuate less dramatically than UVB, they still peak during midday and in summer. Health guidelines in countries like Australia recommend wearing sunscreen when the UV index is 3 or above, but not necessarily every day.

Personal factors also influence the need for sunscreen indoors. People with darker skin, who have more melanin, may need less protection from incidental UV exposure but might still require UVA protection to prevent pigmentation. Those using skincare products that increase UV sensitivity, like alpha hydroxy acids, or those with specific medical conditions, such as photosensitivity or a family history of skin cancer, may also get particular benefit from wearing sunscreen indoors.

As to the downsides? There are some drawbacks to wearing sunscreen indoors, including cost, the effort required for application, and the risk of clogged pores. Though health concerns related to sunscreen are generally minor, they may tip the balance against wearing it if UV exposure is minimal.

For more on all of this plus visual teaching aids, enjoy:

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Want to learn more?

You might also like:

Do We Need Sunscreen In Winter, Really? ← we tackle the science behind the answer to this similar* question

_{*But different, because now we need to take into account such things as axial tilt, the sun’s trajectory through the atmosphere (and thus how much gets reflected, refracted, diffused, etc—or not, as the case may be).}

Take care!